Tracking system load is a basic requirement in the operation, maintenance, efficient scheduling and control of power systems. In particular, with the development of a smart grid that allows power producers and users to respond intelligently to the actual system and market conditions, load forecasting is becoming more and more important. First, it provides useful information for reducing the cost. In many daily operations of the power factory, such as unit commitment, economical dispatch, and automatic general control, knowing the system load up to a short time span in the future is crucial to taking actions. Second, it can facilitate decision and management. Knowing the maximum system load can help maintenance scheduling and hydro-thermal coordination. Third, it can guarantee secure and uninterrupted power supply for energy commercialization.